A vehicle which has a pair of coaxially-arranged left and right wheels and moves while keeping an inverted state is known. For example, an inverted two-wheel moving robot which autonomously moves while keeping an inverted state is disclosed in Patent document 1 (Japanese Unexamined Patent Application Publication No. 2006-123014). A coaxial two-wheel vehicle which moves while keeping the balance in a state in which a human stands on a step is disclosed in Patent document 2 (Japanese Unexamined Patent Application Publication No. 2006-315666).
FIG. 10 is a diagram showing a configuration of a controller of the inverted two-wheel moving robot disclosed in the Patent document 1.
In FIG. 10, a reference number 1001 denotes a friction observer; a reference number 1002 denotes a target state generator; a reference number 1003 denotes state feedback gains; and a reference number 1004 denotes an inverted robot.
An angular speed reference input is input to the friction observer 1001, and the friction observer 1001 calculates a friction of a motor and a friction between a wheel and a road as an estimated friction and outputs the estimated friction.
The angular speed reference input and the estimated friction are input to the target state generator 1002, and the target state generator 1002 calculates a target state of the inverted robot 1004, which is the subject to be controlled, and outputs the calculation result.
A signal obtained by subtracting a state variable of the inverted robot 1004 from the target state is input to the state feedback gains 1003, and the state feedback gains 1003 calculate state feedback signals, which make the inverted robot 1004 move in a desired manner, based on the input signal, and output the state feedback signals.
The inverted robot 1004 is driven by the sum of the state feedback signals and the estimated friction.
As mentioned above, the conventional method of the inverted two-wheel moving robot controls the motions of the inverted robot 1004 based on a linearized model which is obtained by linearlizing the inverted robot 1004, which is the subject to be controlled, in the vicinity of a desired posture.